It is known that an artificial intervertebral disc may be provided for replacing diseased or damaged disc for the treatment of spinal or back pain diseases. Conventional disc prostheses generally consist of two metal endplates and a flexible core in between mimicking the nucleus of the disc.
U.S. Pat. No. 4,309,777 disclosed a disc having a plurality of springs positioned between an upper disc and a lower disc. Each upper or lower disc is formed as a short cylinder. Whenever bending the body, the two discs may be dogged with each other to lock their flexible movement to thereby influence the smooth movement of the spine.
U.S. Pat. No. 5,370,697 disclosed an elastic separator in between an upper and a lower support. However, the acute edges (17) on the upper and lower supports may damage the spinal nerve especially when the insert part (5) is bursted.
U.S. Pat. No. 5,562,738 disclosed a ball and socket for the disk device, which however does not provide any outer protective cover (or covers) for restraining the insert materials in the disk once burst or bulkiness is caused.
U.S. Pat. No. 5,674,296 disclosed a resilient nucleus surrounded by two concaval-convex shells in the disc prosthesis. The nucleus may be freely slipped within the two shells to influence its supporting stability of the disc.
U.S. Pat. No. 5,824,093 disclosed one or two hydrogel capsules in the prosthetic disc. Since the capsules (10) are formed as elongated shaped and easily slipped, they can not support the body weight homogeneously and stably.
U.S. Pat. No. 6,368,350 disclosed two bearing surfaces formed in the disc prosthesis for a rotational freedom. However, once the two bearing surfaces are abnormally biased or dislocated, how can they be normally restored automatically? Meanwhile, it is lacking of any cushioning mechanism for mimicking the disc nucleus.
U.S. Pat. No. 6,395,032 disclosed a flexible seal extending between two opposing plates of the disc prosthesis having liquid provided in a closed chamber between the two plates. There is no safety means provided for preventing from the burst of the disc. A catastrophe may occur to seriously injure the patient once the disc is bursted.
The present inventor has found the drawbacks of the conventional prosthesis discs and invented the present prosthetic intervertebral disc for vividly simulating a true disc.